#' @name present
#' @title Birth rates from 1940 to 2002
#' @description Number of male and female births, sex ratio at birth, and number
#'     of excess males: United States, 1940–2002.
#' @source Mathews, TJ and Hamilton, B.E. Trend analysis of the sex ratio at
#'     birth in the United States. National Vital Statistics Reports. vol 53,
#'     no. 20, pp 1 - 17, 2005. http://www.cdc.gov/nchs/data/nvsr/nvsr53/nvsr53_20.pdf
#' @format A data frame with 63 observations on the following 3 variables.
#' year: a numeric vector, 1940-2002
#' boys: a numeric vector, number of male births
#' girls: a numeric vector, number of female births
#' @docType data
NA

#' @name sat
#' @title SAT verbal and math scores
#' @format 164 observations of 3 variables:
#' Verbal.SAT: a numeric vector, student's SAT verbal score.
#' Math.SAT: a numeric vector, student's SAT math score
#' Sex: a character vector with F = female and M = male
#' @docType data
NA
